When arsine makes the difference: chelating phosphino and bridging arsinoarylthiolato gallium complexes

The (organo)gallium compounds GaCl{(SC6H4-2-PPh2)-kappa2S,P}2 (1), Ga{(SC6H4-2-PPh2)-kappa2S,P}{(SC6H4-2-PPh2)-kappaS}2 (2), GaMe2{(SC6H4-2-PPh2)-kappa2S,P} (3), GatBu2{(SC6H4-2-PPh2)-kappa2S,P} (4), GatBu{(SC6H4-2-PPh2)-kappa2S,P}{(SC6H4-2-PPh2)-kappaS} (5), [GaMe2{(mu2-SC6H4-2-AsPh2)-kappaS}]2 (6), and GatBu{(SC6H4-2-AsPh2)-kappa2S,As}{(SC6H4-2-AsPh2)-kappaS} (7) were obtained from the reaction of 2-EPh2C6H4SH (E = P (PSH), As (AsSH)) with GaCl3 (1, 2) or GaR3 (R = Me, tBu; 3-7) in different molar ratios and under different reaction conditions. Compound 2 was also obtained from Li(PS) and GaCl3 (3.5:1). While a monomeric structure with a chelating phosphinoarylthiolato ligand is observed in GaMe2{(SC6H4-2-PPh2)-kappa2S,P} (3), a dimeric arsinoarylthiolato-bridged complex [GaMe2{(mu2-SC6H4-2-AsPh2)-kappaS}]2 (6) is obtained with the corresponding AsS- ligand. B3LYP/6-31G(d) calculations show that although the dimer is thermodynamically favored for both ligands, the formation of 3 is due to the combination of higher stability of the chelate compared with the monodentate phosphorus ligand and a higher barrier for the ring opening of the PS- than of the AsS- chelate.